Don't require argv file list if specified in taprc

Previously, checking for specified test files was done by looking at
argv.length.  So, if a `files` config was specified in taprc, it would
work if a `--` was passed in on the command line, but otherwise would
dump the usage message one sees when running `tap` with no arguments (or
would wait for stdin if not run on a TTY).

Fix #438

bin/run.js

@@ -52,11 +52,6 @@ const coverageServices = [
 const main = _ => {
   const args = process.argv.slice(2)
 
-  if (!args.length && isTTY) {
-    console.error(usage())
-    process.exit(1)
-  }
-
   // set default args
   const defaults = constructDefaultArgs()
 
@@ -86,6 +81,11 @@ const main = _ => {
 
   options.files = globFiles(options.files)
 
+  if (!args.length && !options.files.length && isTTY) {
+    console.error(usage())
+    process.exit(1)
+  }
+
   // this is only testable by escaping from the covered environment
   /* istanbul ignore next */
   if ((options.coverageReport || options.checkCoverage) &&

tap-snapshots/test-run.js-TAP.test.js

@@ -18,6 +18,23 @@ ok 1 - test/cli-tests/ok.js # {time}
 
 `
 
+exports[`test/run.js TAP rc file specifies test files > expected stdout 1`] = `
+TAP version 13
+# Subtest: test/cli-tests/via-rcfile.js
+    # Subtest: child
+        ok 1 - this is fine
+        1..1
+    ok 1 - child # {time}
+    
+    1..1
+    # {time}
+ok 1 - test/cli-tests/via-rcfile.js # {time}
+
+1..1
+# {time}
+
+`
+
 exports[`test/run.js TAP stdin with file > undefined 1`] = `
 TAP version 13
 ok 1 - test/cli-tests/foo.test.js # {time} {

test/run.js

@@ -251,6 +251,28 @@ jobs: 3
   t.end()
 })
 
+t.test('rc file specifies test files', t => {
+  const testfile = tmpfile(t, 'via-rcfile.js', `
+    'use strict'
+    require(${tap}).test('child', t => {
+      t.pass('this is fine')
+      t.end()
+    })
+  `)
+
+  const rc = tmpfile(t, 'taprc', `
+files: [ ${testfile} ]
+reporter: tap
+  `)
+
+  const c = run([], { env: { TAP_RCFILE: rc }}, (er, o, e) => {
+    t.equal(er, null)
+    t.matchSnapshot(clean(o), 'expected stdout')
+    t.equal(e, '')
+    t.end()
+  })
+})
+
 t.test('stdin', t => {
   const tapcode = 'TAP version 13\n1..1\nok\n'